Spring driven hydraulic actuator

ABSTRACT

An actuator which uses a double-ended hydraulic spring to propel an internal combustion engine poppet valve back and forth between a closed and an open positions. Timed delivery of supplemental pressure to a separate latching piston provides a means to fully &#34;re-cock&#34; the rebounding springs in each position. Activation is accomplished by releasing the supplemental pressure to allow the compressed fluid spring to propel the poppet valve in either one of two directions. A valve arrangement is also provided to allow a timed bypass of fluid around the latching piston during most of its transitioning to minimize the quantity of high pressure fluid consumption to that which is required to overcome friction losses.

SUMMARY OF THE INVENTION

The present invention relates generally to bistable actuators and moreparticularly to a two position, bistable, asymmetrical, fast acting,straight line motion actuator which uses a double-ended hydraulic springto drive an internal combustion engine poppet valve back and forthbetween open and closed positions.

This actuator finds particular utility in opening and closing the gasexchange, i.e., intake or exhaust, valves of an otherwise conventionalinternal combustion engine. Due to its fast acting trait, the valves maybe moved by the fluid pressure from the full closed to the full openposition, and from the full open back to the full closed by the storedpiston energy almost immediately rather than gradually as ischaracteristic of cam actuated valves. The actuator mechanism may findnumerous other applications.

In U.S. Pat. Nos. 3,844,528 to Massie and 4,930,464 to Letsche there areshown electrically controlled hydraulically powered mechanisms foropening and closing an internal combustion engine poppet valves. Bothsuffer from long and therefor slow to react hydraulic lines. The Massiedevice is symmetric in its operation, that is, opening and closing ofthe engine valve occur in the same way. Massie employs a sleeve valvesurrounding the power cylinder to selectively gate engine lubricatingoil to the opposite sides of a power piston. In addition to the long andtherefor slow to react hydraulic lines, the variable volume chambers onopposite sides of the power piston are relatively large and requireexcessive time to be filled and emptied when driving the valve back andforth. Massie is simply too slow to be an effective engine valvecontrol. Letsche, except for a modification shown only in FIG. 7, isalso symmetric in its operation. Letsche briefly opens the same controlvalve to initiate valve motion regardless of the direction of motion.This opening of the valve releases high pressure fluid from one pistonface allowing a compressed one of two symmetric springs to drive theengine valve from one position to the other. As the valve approaches itssecond position, the other of the springs is compressed (and the firststretched) serving both to slow valve movement, and also to storepotential energy for the return trip. As the valve is transitioning fromone position to the other, fluid is allowed to flow from one piston faceto the other by way of a bypass conduit. In the asymmetrical version ofFIG. 7, Letsche applies additional force to open the engine valve byapplying high pressure fluid to one end of the device.

In our U.S. Pat. No. 4,831,973 as well as the Richeson U.S. Pat. No.4,883,025 and Gotschall U.S. Pat. No. 4,749,167 there is found a generalteaching of the concept of employing a pneumatic damping piston forslowing the motion of an internal combustion engine valve near thecompletion of its traversal from one stable state to another, andsubsequently utilizing the potential energy accumulated by the dampingpiston for powering the engine valve back toward the first of its stablestates. These devices either employ an electromagnet or a permanentmagnet in conjunction with a coil to temporarily neutralize the field ofthat permanent magnet as latching mechanisms for holding the valve ineach of the two end positions. These devices are symmetrical in thesense that the same propulsive forces and the same damping forcesoccasioned by the same hardware are encountered regardless of thedirection of travel.

In our copending application entitled SPRING DRIVEN HYDRAULIC ACTUATORfiled on even date herewith, there is disclosed an actuator whichutilizes an air chamber to damp piston motion in either direction andthen uses the just compressed air to power the piston back in theopposite direction. The invention of this copending application utilizesa hydraulic latch to hold the piston in one or the other extremepositions against the pneumatic force. The actuator of that applicationhas a latching piston in a power module. The latching piston has aninterconnecting shaft extending into a spring module in which a secondpiston functions as part of the hydraulic fluid spring assembly. Theshaft extends beyond these modules and interconnects with an enginepoppet valve. A shaft extension through the latching piston provides ameans to power a reciprocating fluid control valve by means ofinterconnected helical springs. These springs provide forces on alatching armature which are in opposition to the forces applied to thatarmature by a pair of latching magnets.

In our copending application entitled PNEUMATIC PRELOADED ACTUATOR, Ser.No. 680,721 filed on even date herewith, there is disclosed an actuatorhaving hydraulic latching at each extreme of its motion with a pneumaticspring which is cocked as a piston nears the end of each of itstraversals to subsequently power the piston back in the other direction.Supplementary power to make up for system losses such as friction issupplied by supplemental hydraulic pressure being valved in to thelatching chamber near the end of piston travel in one direction.

In Richeson U.S. Pat. No. 4,974,495 as well as the copending RichesonU.S. patent application Ser. No. 07/557,377 there are disclosed fastacting valve actuators for actuating intake or exhaust valves ininternal combustion engines of a type which are hydraulically poweredand command triggered. The actuators of these disclosures go a long waytoward solving the problem of long hydraulic lines characteristic ofdevices such as disclosed in the above mentioned Letsche and Massiepatents. These actuators include a cylinder with a power piston having apair of opposed working surfaces or faces which is reciprocable withinthe cylinder along an axis between first and second extreme positions. Acylindrical control valve is located radially intermediate the reservoirand the cylinder, and is movable upon command to alternately supply highpressure fluid from a reservoir of high pressure hydraulic fluid to oneface and then the other face of the power piston causing the piston tomove from one extreme position to the other extreme position. Thecylindrical control valve may be a shuttle valve which is reciprocablealong the axis of the power piston between extreme positions withcontrol valve motion along the axis in one direction being effective tosupply high pressure fluid to move the piston in the opposite direction.Both the control valve and the piston are stable in both of theirrespective extreme positions and the control valve is spring biasedtoward a position intermediate the extreme positions. The latter portionof piston motion during one operation of the valve actuator is effectiveto cock this spring and bias the control valve preparatory to the nextoperation. A significant distinction between the patent and the pendingapplication is that the patented arrangement utilizes high pressurehydraulic fluid to power the piston in each direction while the pendingapplication utilizes an air chamber to damp piston motion in onedirection and then uses the compressed air to power the piston back inthe opposite direction.

The entire disclosures of all of the above identified copendingapplications and patents are specifically incorporated herein byreference.

In the last mentioned copending application, a piston is powered from afirst (engine valve closed) position by high pressure hydraulic fluid ina manner similar to the abovementioned Richeson U.S. Pat. No. 4,974,495.As in that application, a relatively constant high pressure source ismaintained close to the piston and the fluid ducting and valving paththerebetween has a very high ratio of cross-section to length. Thismakes the valve very fast acting to open an engine valve andsignificantly reduces losses as compared to conventional hydraulicsystems. As the piston approaches the engine valve-open position, thepiston assembly including the engine valve are slowed or damped andpiston assembly kinetic energy is converted to and stored as potentialenergy. This potential energy is subsequently utilized to drive thepiston back to its initial or valve-closed position.

Also in the lastmentioned copending application, a hydraulic actuatorutilizes a double hydraulic spring assembly, a power piston and a valvearrangement for supplying supplemental fluid under high pressure to thepower piston. The actuator operates on the principle of holding aninternal piston in either of two stable positions by valved-in highpressure fluid which provides a force opposing that of an external fluidspring. The valved-in pressure functions to cock the fluid spring ineither of its two positions. The fluid springs are utilized as energyrecovery devices and "bounce" the actuator piston back and forth betweenthem with the supplemental pressure being added only toward the end ofthe travel to make certain that the actuator does transit its fulldistance and does fully re-cock the other fluid spring at the end of itstravel. The supplemental pressure is valved-in behind the piston at thelatest possible time to keep the overall transition efficiency as highas possible. The actuator will remain in either of its two restpositions as long as the supplemental pressure continues to apply aseating force to the actuator piston. To initiate a transition from oneposition to the other, the supplemental pressure is simply removed sothat the energy stored in the fluid spring is released to power theactuator to its next position.

A significant distinction between the last mentioned patent andcopending application on the one hand and the present invention on theother is that the prior arrangements utilize high pressure hydraulicfluid to power the piston in one or both directions while the presentapplication utilizes a hydraulic chamber to damp piston motion in eitherdirections and then uses the energy stored in the compressed hydraulicfluid to power the piston back in the opposite direction. The presentinvention utilizes a hydraulic latch to hold the piston in one or theother extreme positions against the hydraulic force.

In contradistinction to the earlier-described devices, the actuator ofthe present invention has a latching piston in a power module. Thislatching piston has an interconnecting shaft extending into a springmodule in which a second piston functions as part of the hydraulic fluidspring assembly. The shaft extends beyond these modules andinterconnects with an engine poppet valve. A shaft extension through thelatching piston provides a means to power a reciprocating fluid controlvalve by means of interconnected helical springs. These springs provideforces on a latching armature which are in opposition to the forcesapplied to that armature by a pair of latching magnets.

Among the several objects of the present invention may be noted theprovision of an actuator powered primarily by hydraulic fluid compressedwhile damping previous actuator motion; the provision of a bistableactuator having symmetric hydraulic damping and symmetric hydrauliclatching; the provision of a poppet valve actuator of enhancedefficiency; the provision of an actuator employing a reciprocatinghydraulic piston which functions both as a power piston and as a dampingpiston; and the provision of an electronically controllablehydraulically powered, hydraulically latched valve actuating mechanismfor use in actuating the poppet valves of an internal combustion engine.These as well as other objects and advantageous features of the presentinvention will be in part apparent and in part pointed out hereinafter.

In general, a bistable engine valve actuator has a mechanism portionreciprocable between each of two stable positions and has areplenishable source of high pressure hydraulic fluid along with a latchsymmetrically operable in each of the stable positions for temporarilypreventing translation of the mechanism portion. The high pressure fluidsource includes a cylinder having a pair of opposed fixed end walls, apair of pistons reciprocable within the cylinder to define therewiththree variable volume chambers, one comprising a high pressure sourcechamber between the pistons and one each functioning as low pressurerelief chambers between a piston and one cylinder end wall, and a pairof compression springs interposed between a piston and a correspondingcylinder end wall for urging the pistons toward one another. The latchincludes a latching piston having a pair of opposed faces and positionedclosely adjacent the source of high pressure fluid, and a control valvefor selectively supplying high pressure fluid to one of the latchingpiston faces thereby preventing translation of the portion of themechanism which mechanism portion includes the latching piston. There isa first variable volume chamber in which hydraulic fluid is compressedduring translation of the mechanism portion in one direction withcompression of the fluid slowing the mechanism portion translation inthat direction, and this first variable volume chamber retains thecompressed fluid for later driving the mechanism portion back in anopposite direction. There is also a second variable volume chamber inwhich fluid is compressed during translation of the mechanism portion inopposite direction with compression of the fluid slowing the mechanismportion translation in said opposite direction. This second variablevolume chamber also retains the compressed fluid for later driving themechanism portion back in the first direction. A source of high pressurefluid is provided to maintain the minimum fluid pressure in the firstand second variable chambers at least a predetermined level.

Also in general and in one form of the invention a bistableelectronically controlled hydraulically driven, hydraulically latchedtransducer has an armature reciprocable between first and secondpositions with a hydraulic arrangement for holding the armature in eachof the first and second positions. The hydraulic latching arrangementincludes a bistable generally cylindrical control valve encircling atleast a portion of the armature. This control valve is operable in oneof its stable states to supply high pressure hydraulic fluid to forcethe armature in one direction and in the other of its stable states tosupply high pressure hydraulic fluid to force the armature in anopposite direction. There is a first chamber in which fluid iscompressed during motion of the armature from the first position to thesecond position with compression of the fluid slowing armature motion asit nears the second position and a similar second chamber in which fluidis compressed during motion of the armature from the second position tothe first position. The control valve remains in one stable state totemporarily prevent reversal of armature motion when the motion of thearmature has slowed to a stop later returning to the other of its stablestates on command to allow the fluid compressed in the chamber to returnthe armature to the first position. A replenishable source of highpressure hydraulic fluid is located closely adjacent the armature andcomprises a cylinder with a pair of opposed fixed end walls and a pairof pistons reciprocable within the cylinder to define therewith threevariable volume chambers.

The chamber between the pistons functions as a high pressure sourcewhile those between the pistons and corresponding cylinder end wallsfunction as low pressure relief chambers. A pair of compression springsurge the pistons toward one another.

Still further in general, a bistable electronically controlledtransducer has an armature which is reciprocable between first andsecond positions. A first hydraulic arrangement powers the armature fromthe first position to the second position and a second hydraulicarrangement powers the armature from the second position back to thefirst position. A first hydraulic spring is compressed during motion ofthe armature from the first position to the second position withcompression of the first hydraulic spring slowing armature motion as itnears the second position. A second hydraulic spring is compressedduring motion of the armature from the second position to the firstposition with compression of the second hydraulic spring slowingarmature motion as it nears the first position. The hydraulicarrangement maintains pressure on the armature to temporarily preventreversal of armature motion when the motion of the armature has slowedto a stop, and is disableable on command to allow the compressed firsthydraulic spring to return the armature to the first position or toallow the compressed second hydraulic spring to return the armature tothe second position. In the preferred embodiment, the first hydraulicspring comprises the second hydraulic arrangement and the secondhydraulic spring comprises the first hydraulic arrangement.

BRIEF DESCRIPTION OF THE DRAWING

FIGS. 1-6 show, in sequence, the operation of the actuator with likenumbered "a" and "b" figures show the actuator in the same position, butwith the sections being taken at right angles to one another along linesa--a and b--b respectively of FIG. 8. More particularly:

FIG. 1a is a longitudinal cross-section view of an actuator in theextended or "valve-open" position according to the invention in oneform;

FIG. 1b is a cross-sectional view similar to FIG. 1a, but showing thelow pressure galley valving;

FIG. 2a is a cross-sectional view along the same line as FIG. 1a,showing the actuator with the fluid valve released to the right shuttingoff high pressure fluid to the left face of the latching piston;

FIG. 2b is a cross-sectional view along the same line as FIG. 1b showingfluid flow around the piston by way of the fluid galley;

FIG. 3a is a cross-sectional view along the same line as FIG. 1a, butshowing the piston about midway in its travel and with all high pressureto the piston shut off;

FIG. 3b is a cross-sectional view along the same line as FIG. 1b, butshowing the piston displacing the fluid into the low pressure galley andfluid return to the back side of the piston as the fluid valve continuesto move to the right;

FIG. 4a is a cross-sectional view along the same line as FIG. 1a, butwith the fluid valve having opened the high pressure/low pressure portsto provide times supplemental power from the accumulator to drive thepiston all the way to the left;

FIG. 4b a cross-sectional view along the same line as FIG. 1b, but thevalving has now shut off the low pressure galley from the piston;

FIG. 5a is a cross-sectional view along the same line as FIG. 1a showinghow the accumulator pistons have now expended their high pressure fluidand are ready to be recharged;

FIG. 6a is a cross-sectional view along the same line as FIG. 1a, butshowing the accumulator pistons fully recharged and ready for the nexttransit;

FIG. 7 illustrates the double ended hydraulic fluid spring assemblyabout midway in position; and

FIG. 8 is a view in cross-section along lines 8--8 of FIG. 1a.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawing.

The exemplifications set out herein illustrate a preferred embodiment ofthe invention in one form thereof and such exemplifications are not tobe construed as limiting the scope of the disclosure or the scope of theinvention in any manner.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings generally, an electronically controllablevalve actuating mechanism is illustrated for use in an internalcombustion engine of the type having engine intake and exhaust valvessuch as illustrative valve 21 with elongated valve stems such as 37. Theactuator has a pair of stable positions corresponding to the enginevalve open and engine valve closed positions respectively. The actuatorincludes a power piston 1 having a pair of opposed faces 39 and 41defining variable volume chambers 6 and 23 respectively. Power piston 1is reciprocable along axis 43 and is coupled to engine valve 21. Aresilient damping arrangement which includes the power piston 1symmetrically imparts a continuously increasing decelerating forces asthe engine valve 21 approaches either of the valve-open and valve-closedpositions. A hydraulic latching arrangement is operable on command tohold the power piston and engine valve in each of the stable positionsand is operable on a subsequent command to allow the resilient dampingmeans (in particular, the fluid pressure in chamber 15 or 16 of FIG. 7)to power the piston back from either of the valve-open and valve-closedpositions to the other position. The commands take the form ofelectrical signals to coils 12 a or 12b which neutralize the holdingforce of permanent magnets 29 and 31. The damping means (FIG. 7)comprises a cylinder having a pair of opposed closed end walls 45 and 47within which the power piston 14 reciprocates. Piston 14 defines twovariable volume chambers 15 and 16 the sum of the volumes of which issubstantially constant. The mechanism further including a coilcompression spring 17 for urging the power piston 14 and shaft 10 in adirection to close the corresponding engine valve 21.

The hydraulic latch includes a hydraulic cylinder and latching piston 1which is fixed by common shaft 10 to the power piston 14 and moveswithin the cylinder to define in conjunction therewith a pair ofvariable volume chambers 6 and 23. A control valve 3 regulates theescape of hydraulic fluid from these variable volume chambers. Thecontrol valve is of a generally cylindrical shape coaxial with axis 43and at least partially surrounds the latching piston 1. The actuator isprimarily powered by fluid acting on power piston 14. FIGS. 1a and 4ashow that, at a point near the extreme positions of piston 1, motiveforce from the hydraulic pressure on latching piston 1 is applied toforce the mechanism in either extreme position so as to cock thehydraulic spring.

The actuator has a double acting return spring (shown in FIG. 7) withthat spring being maximally compressed in FIGS. 1 and 6, the extremeright and left positions of the latching piston 1 respectively. In FIG.1, the actuator piston 1 is in the extreme position to the right withlatch plate 2 and control valve 3 in their leftmost positions. Noticethat the helical spring 13 is extended and the helical spring 11 iscompressed, both stressed and ready to drive the latch plate 2 and thecontrol valve 3 toward the right when coil 12a is energized. In FIGS. 1aand 1b, the control valve 3 allows high pressure fluid from galley 4 toenter cylinder 5 and pass down conduit 25 on into chamber 6 forcingpiston 1 toward the right. The right side of piston 1 is vented throughconduit 27 to the low pressure fluid sink 7. The high pressure in cavity5 working against the low (sink 7) pressure on the outboard faces ofpistons 8 drives those pistons away from one another compressing thesprings 9 in FIGS. 1a and 1b.

In FIG. 2a, the coil 12a has been energized neutralizing the holdingforce of permanent magnet 29, and the ferromagnetic plate 2 and controlvalve 3 are being propelled toward the right by the combined efforts ofthe springs 11 which is expanding toward its unstressed state and 13which is contracting toward its unstressed state, and the attractiveforce of permanent magnet 31 on the plate 2. As the control valve 3moves toward the right, it closes both conduits 27 and 25. At the sametime, a comparison of FIGS. 1b and 2b reveals shows that valve 3 alsoports both sides of the latching piston 1 to the low pressure galley 7by way of ports 28 and 29. Fluid races from the left to the right sideof piston 1 as the spring (FIG. 7) drives the piston toward the left inFIG. 2a. Check valve 36 opens to supply low pressure fluid to cavity 23as piston 1 moves to the left.

Motion of the piston 1, latch plate 2 and shaft 10 continues expandingspring 11 and compressing the spring 13. Later on in a following cycle,spring 13 will propel plate 2 and valve 3 back toward the left. Thus,motion of piston 1 generates the force for driving the armature plate 2that will properly valve the actuator upon command sent to latch coils12a and 12b.

The force causing piston 1 to move to the left is derived by thedifferential pressure in cavities 15 and 16 shown in FIG. 7. Thisdifferential pressure acts on the differential area between segments 10and 14 of the shaft which compresses or expands the fluid in cavities 15and 16. When the shaft is in one or the other extreme position, onepressure is maximum and the other is minimal. Fluid source 18 suppliesmake-up hydraulic fluid through one-way check valves 19 and 20 therebysetting the minimal pressure at that of the source. This minimalpressure is selected so as to prevent cavitation of the fluid inchambers 15 and 16.

FIGS. 3a and 3b illustrate the valve 3 and piston 1 progressing into thefinal state which will seat poppet valve 21. It should be rememberedthat the bidirectional fluid spring mechanism of FIG. 7 will beinterposed between the valve 21 and the other structure of FIG. 3. Thehydraulic valve ports of conduits such as 25 and 27 of valve 3 which arevisible in FIG. 3a remain closed while those shown in FIG. 3b (28 and29) remain open as the double acting spring 17 moves the shaft 10 to theleft. Check valve 36 also remains open during this time to supply lowpressure fluid to cavity 23 allowing free movement of piston 1.

In FIG. 4a, the high pressure source is now ported from cavity 5 intochamber 23 on the right side of piston 1 and closes check valve port 32and check valve 36 while the cavity 6 on the left (advancing) face ofpiston 1 is ported by way of conduit 33 to the low pressure chamber 7.This late portion of high pressure hydraulic fluid into cavity 23supplies the fluid to move piston 1 into the final position of itsmotion to the left, thus using only a small volume of high pressurefluid and hence a much reduced amount of hydraulic energy. Thispressurization of cavity 23 causes the spring 17 of FIG. 7 to be cockedtoward one extreme position and the pressure in cavity 15 to peak, bothtending to slow or damp the final closing of poppet valve 21. Thepressure in cavity 15 acts on the difference between the circularcross-sectional areas of shaft 10 and enlarged portion 14. Similarly,the pressure in cavity 16 acts in an opposite direction on thedifference between these two areas. The peak pressure differentialbetween cavities 15 and 16 operating on the differential area of shaft10 and shaft portion 14 will supply the force to open poppet valve 21 onthe next transition. The hydraulic ports of control valve 3 visible inFIG. 4a are now open while those visible in FIG. 4b are closed. Thisshort term supply of fluid via conduit 35 and sinking via conduit 33 aremade possible mainly from the differential motion of pistons 8 and 22collapsing toward one another under the urging of springs 9. This isapparent from a comparison of FIGS. 3a and 4a.

As piston 1 is driven to its full limit toward the left, damping of themotion of shaft 10 and gentle seating of poppet valve 21 occurs as thepiston 1 approaches its seat 24 and chamber 6 shrinks to essentiallyzero volume. This damping is due in part by the spring 17 of FIG. 7being compressed and absorbing the kinetic energy of actuator motion. Inthe transition from FIG. 4a to FIG. 5a it will be observed that thepistons 8 and 22 reach their near limit of collapsing motion by the timeengine poppet valve 21 is seated. A short time later the pistons 8 and22 are re-cocked (expanded away from one another compressing springs 9)by an external pump which supplies high pressure hydraulic fluid togalley 4. This pump has a low pressure return from galley 7. This schemeof sourcing and sinking the hydraulic fluid via the chambers containingpistons 8 and 22 provides very fast fluid action with slower rechargingof these chambers between actuator transitions.

An analogous sequence of events occurs in moving piston 1 to the rightin these figures thus unseating and opening valve 21. The goal ofgreatly reducing the required external energy to open and close thevalve has been attained.

From the foregoing, it is now apparent that a novel hydraulic springdriven actuator has been disclosed meeting the objects and advantageousfeatures set out hereinbefore as well as others, and that numerousmodifications as to the precise shapes, configurations and details maybe made by those having ordinary skill in the art without departing fromthe spirit of the invention or the scope thereof as set out by theclaims which follows.

What is claimed is:
 1. A bistable actuator having a mechanism portionreciprocable between each of two stable positions and comprising:areplenishable source of high pressure hydraulic fluid; meanssymmetrically operable in each of the stable positions for temporarilypreventing translation of the mechanism portion including a latchingpiston having a pair of opposed faces and positioned closely adjacentthe source of high pressure fluid, and a control valve for selectivelysupplying high pressure fluid to one of the latching piston facesthereby preventing translation of the portion of the mechanism includingthe latching piston; a first variable volume chamber in which fluid iscompressed during translation of the mechanism portion in one direction,compression of the fluid slowing the mechanism portion translation insaid one direction, said first variable volume chamber retaining thecompressed fluid to drive the mechanism portion back in a directionopposite said one direction; a second variable volume chamber in whichfluid is compressed during translation of the mechanism portion in saidopposite direction, compression of the fluid slowing the mechanismportion translation in said opposite direction, said second variablevolume chamber retaining the compressed fluid to drive the mechanismportion back in said one direction; and a source of high pressure fluidfor maintaining the minimum fluid pressure in the first and secondvariable chambers at least a predetermined level.
 2. The bistableactuator mechanism of claim 1 wherein the replenishable source of highpressure hydraulic fluid comprises a cylinder having a pair of opposedfixed end walls, a pair of pistons reciprocable within the cylinder todefine therewith three variable volume chambers, one comprising a highpressure source chamber between the pistons and one each functioning aslow pressure relief chambers between a piston and one cylinder end wall,and a pair of compression springs for urging the pistons toward oneanother, each compression spring being interposed between a piston and acorresponding cylinder end wall.
 3. An electronically controllable valveactuating mechanism for use in an internal combustion engine of the typehaving engine intake and exhaust valves with elongated valve stems, theactuator having a pair of stable positions and comprising;a power pistonhaving a pair of opposed faces defining variable volume chambers, thepower piston being reciprocable along an axis and adapted to be coupledto an engine valve; resilient damping means including the power pistonfor symmetrically imparting continuously increasing decelerating forcesas the engine valve approaches either of the valve-open and valve-closedpositions; hydraulic means operable on command for holding the powerpiston and engine valve in each of the stable positions, and operable ona subsequent command to allow the resilient damping means to power thepiston back from either of the valve-open and valve-closed positions tothe other position.
 4. The electronically controllable valve actuatingmechanism of claim 3 wherein the resilient damping means comprises acylinder having a pair of opposed closed end walls within which thepower piston reciprocates defining two variable volume chambers, the sumof the volumes of which is substantially constant, the mechanism furtherincluding a coil compression spring for urging the power piston in adirection to close the corresponding engine valve.
 5. The electronicallycontrollable valve actuating mechanism of claim 3 wherein the hydraulicmeans comprises a hydraulic cylinder and a latching piston fixed to thepower piston and movable within the cylinder to define in conjunctiontherewith a pair of variable volume chambers, and a control valve forcontrolling the escape of hydraulic fluid from the chambers.
 6. Theelectronically controllable valve actuating mechanism of claim 5 whereinthe control valve is of a generally cylindrical shape and at leastpartially surrounds the latching piston.
 7. A bistable electronicallycontrolled hydraulically driven, hydraulically latched transducer havingan armature reciprocable between first and second positions, hydraulicmeans for holding the armature in each of the first and second positionssaid hydraulic means including a bistable generally cylindrical controlvalve surrounding at least a portion of the armature, the control valvebeing operable in one of its stable states to supply high pressurehydraulic fluid to force the armature in one direction and in the otherof its stable states to supply high pressure hydraulic fluid to forcethe armature in an opposite direction, a first chamber in which fluid iscompressed during motion of the armature from the first position to thesecond position, compression of the fluid slowing armature motion as itnears the second position, a second chamber in which fluid is compressedduring motion of the armature from the second position to the firstposition, compression of the fluid slowing armature motion as it nearsthe first position, the control valve remaining in said one stable stateto temporarily prevent reversal of armature motion when the motion ofthe armature has slowed to a stop, the control valve returning to theother of its stable states on command to allow the fluid compressed inthe chamber to return the armature to the first position.
 8. Thebistable electronically controlled hydraulically driven, hydraulicallylatched transducer of claim 7 wherein the hydraulic means furtherincludes a replenishable source of high pressure hydraulic fluid closelyadjacent the armature and comprising a cylinder having a pair of opposedfixed end walls, a pair of pistons reciprocable within the cylinder todefine therewith three variable volume chambers, one comprising a highpressure source chamber between the pistons and one each functioning aslow pressure relief chambers between a piston and one cylinder end wall,and a pair of compression springs for urging the pistons toward oneanother, each compression spring being interposed between a piston and acorresponding cylinder end wall.
 9. A bistable electronically controlledtransducer having an armature reciprocable between first and secondpositions, first hydraulic means for powering the armature from thefirst position to the second position, second hydraulic means forpowering the armature from the second position back to the firstposition, a first hydraulic spring which is compressed during motion ofthe armature from the first position to the second position, compressionof the first hydraulic spring slowing armature motion as it nears thesecond position, a second hydraulic spring which is compressed duringmotion of the armature from the second position to the first position,compression of the second hydraulic spring slowing armature motion as itnears the first position, hydraulic means maintaining pressure on thearmature to temporarily prevent reversal of armature motion when themotion of the armature has slowed to a stop, the hydraulic means beingdisableable on command to allow the compressed first hydraulic spring toreturn the armature to the first position and disableable on command toallow the compressed second hydraulic spring to return the armature tothe second position.
 10. The bistable electronically controlledtransducer of claim 9 wherein the first hydraulic spring comprises thesecond hydraulic means and the second hydraulic spring comprises thefirst hydraulic means.
 11. An electronically controllable valveactuating mechanism for use in an internal combustion engine of the typehaving engine intake and exhaust valves with elongated valve stems, theactuator having a pair of stable positions and comprising;a power pistonhaving a pair of opposed faces defining variable volume chambers, thepower piston being reciprocable along an axis and adapted to be coupledto an engine valve; hydraulic damping means including the power pistonfor imparting a continuously increasing decelerating force as the enginevalve approaches either of the valve-open and valve-closed positions;hydraulic means operable on command for holding the power piston andengine valve in each of the stable positions, and operable on command toallow the hydraulic damping means to power the piston back from eitherof the valve-open and valve-closed positions to the other position; anda high pressure hydraulic fluid source operable when the engine valve isnear either one of the valve-open and valve-closed positions for forcingthe power piston and engine valve into a stable position.
 12. Theelectronically controllable valve actuating mechanism of claim 11wherein the hydraulic damping means converts kinetic energy of themoving piston and engine valve into potential energy during damping andutilizes that potential energy to propel the power piston in theopposite direction on the next subsequent command to power the pistonback from either of the valve-open and valve-closed positions to theother position.